In the metallurgical field it is not uncommon to provide steel sheets or strip, steel-workpieces generally, and finished products of steel, like fasteners and similar elements, with metal or metalizing coatings to protect the steel against corrosion. Typical of the coatings which can be applied are galvanically-deposited zinc, mechanically or dip-deposited zinc, correspondingly formed coatings of zinc alloys, or chromatized or phosphatized or passivated zinc coatings on steel or on another metal.
It is not uncommon to provide such coatings with a lacquer as an additional protection against environmental effects and in an after-treatment, usually involving a dipping of the part in the lacquer.
However, the use of a lacquer is not always desirable or advantageous as will be developed below.
Typical of the parts handled in this manner are screws, nuts, fastening elements of other types like hinges, connectors, hook-type fasteners and the like, and all kinds of hardware, fixtures and fittings, including door, cabinet, kitchen, commercial, industrial and agricultural hardware and fittings.
In a typical after-treatment following the application of the zinc coating with a passivation treatment and/or a chromate treatment (chromatizing), the part may be dipped into an organic treatment medium. A typical medium for this purpose can be an aqueous organic synthetic resin dispersion containing corrosion inhibitors or film-forming agents to provide a corrosion barrier.
This protects the zinc coating against corrosion. Prior techniques of this type, however, have not been fully satisfactory, usually because the duration of effectiveness of the after-treatment was not sufficient.
It is also known to treat the zinc coating with a chromic acid containing agent forming an inorganic post-dipping medium. This has the disadvantage that chromic acid systems are environmental pollutants.